[Purposes] This study aims to establish the damage constitutive equation of carbonaceous mudstone under dry-wet cycles. [Methods] Nuclear magnetic resonance tests are carried out on carbonaceous mudstones undergoing 0, 5, 10, and 15 dry-wet cycles, so as to explore the pore evolution law of carbonaceous mudstone. Uniaxial compression tests are carried out on carbonaceous mudstone with dry-wet damage, so as to study the influence of dry-wet cycles on the mechanical properties of rock. On this basis, the Weibull distribution function is used to characterize the damage evolution of rock, and the damage constitutive equation of carbonaceous mudstone is established by considering the pore deformation of carbonaceous mudstone with dry-wet damage. [Findings] With the increase in the number of dry-wet cycles, the pores of carbonaceous mudstone increase, and the size enlarges. The small pores merge and penetrate to form mesopores. Dry-wet cycles aggravate the deterioration of the mechanical properties of carbonaceous mudstone. The peak stress and elastic modulus of carbonaceous mudstone with dry-wet damage decrease, and the ductility increases. The damage constitutive equation can describe the whole process of stress and strain development of carbonaceous mudstone and reflect the nonlinear deformation of rock in the compaction stage. [Conclusions] The damage constitutive model has high applicability and can provide a reference for the construction of carbonaceous mudstone slopes under dry and wet environments.